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.TH PTHREAD_RWLOCK_INIT 3C "Dec 11, 2022"
.SH NAME
pthread_rwlock_init, pthread_rwlock_destroy \- initialize or destroy read-write
lock object
.SH SYNOPSIS
cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ]
#include <pthread.h>

\fBint\fR \fBpthread_rwlock_init\fR(\fBpthread_rwlock_t *restrict\fR \fIrwlock\fR,
     \fBconst pthread_rwlockattr_t *restrict\fR \fIattr\fR);
.fi

.LP
.nf
\fBint\fR \fBpthread_rwlock_destroy\fR(\fBpthread_rwlock_t *\fR\fIrwlock\fR);
.fi

.LP
.nf
\fBpthread_rwlock_t\fR \fIrwlock\fR = \fBPTHREAD_RWLOCK_INITIALIZER\fR;
.fi

.SH DESCRIPTION
The \fBpthread_rwlock_init()\fR function initializes the read-write lock
referenced by \fIrwlock\fR with  the attributes referenced by \fIattr\fR.  If
\fIattr\fR is NULL, the default  read-write lock attributes are used; the
effect is the same as  passing the address of a default read-write lock
attributes object.  Once initialized, the lock can be used any  number of times
without being re-initialized.  Upon successful initialization, the state of the
read-write lock  becomes initialized and unlocked.  Results are undefined if
\fBpthread_rwlock_init()\fR is called specifying an already initialized
read-write lock.  Results are undefined if a read-write lock is used without
first being  initialized.
.sp
.LP
If the  \fBpthread_rwlock_init()\fR function fails, \fIrwlock\fR is not
initialized and the contents of  \fIrwlock\fR are undefined.
.sp
.LP
The \fBpthread_rwlock_destroy()\fR function destroys the read-write lock object
referenced by \fIrwlock\fR and  releases any resources used by the lock.  The
effect of subsequent use of the lock is undefined until the lock  is
re-initialized by another call to \fBpthread_rwlock_init()\fR. An
implementation may cause  \fBpthread_rwlock_destroy()\fR to set the object
referenced by \fIrwlock\fR to an invalid value.  Results are undefined if
\fBpthread_rwlock_destroy()\fR is called when any thread holds \fIrwlock\fR.
Attempting to destroy an uninitialized  read-write lock results in undefined
behaviour.  A destroyed read-write lock object can be re-initialized using
\fBpthread_rwlock_init()\fR; the results of otherwise referencing the
read-write lock object after it  has been destroyed are undefined.
.sp
.LP
In cases where default read-write lock attributes are appropriate, the macro
\fBPTHREAD_RWLOCK_INITIALIZER\fR can be used to initialize read-write locks
that are statically allocated.  The effect is equivalent to dynamic
initialization by a call to  \fBpthread_rwlock_init()\fR with the parameter
\fIattr\fR specified as NULL, except that no error  checks are performed.
.SH RETURN VALUES
If successful, the  \fBpthread_rwlock_init()\fR and
\fBpthread_rwlock_destroy()\fR functions return  \fB0\fR. Otherwise, an  error
number is returned to indicate the error.
.SH ERRORS
The \fBpthread_rwlock_init()\fR and  \fBpthread_rwlock_destroy()\fR functions
will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value specified by \fIattr\fR is invalid.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value specified by \fIrwlock\fR is invalid.
.RE

.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.BR pthread_rwlock_rdlock (3C),
.BR pthread_rwlock_unlock (3C),
.BR pthread_rwlock_wrlock (3C),
.BR pthread_rwlockattr_init (3C),
.BR attributes (7),
.BR standards (7)
